May I suggest using Crypt::CBC which allows you to format your data so it qualifies for Crypt::* encryption. Caution, not all encryption routines on CPAN do Chain Block Ciphering (but most do). For a builtin function, some might point you to crypt, don't be tempted... stay away from crypt :)

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.